This invention relates to a touch response sensor for an electronic musical instrument and, more particularly, to a touch response sensor which produces a signal responsive to the key depressing speed and pressure upon depression of the key.
A keyboard type electronic musical instrument is generally constructed not only to open or close a tone signal source by the key depressing pressure but to control the amplitude of the tone signal in response to the key depressing speed and depressing pressure so as to add a touch response effect i.e., an initial control effect and/or an after-control effect to the instrument.
Heretofore, there was a touch control sensor employing a leaf switch 1 as a switch mechanism for initial control of keys for the instrument utilizing a contact time difference detecting system as shown in FIG. 1, which switch 1 has a movable leaf contact piece 2 driven by a key(not shown) of the instrument, and stationary leaf contact pieces 3 and 4 This leaf switch 1 is connected to a charging and discharging circuit (not shown) composed of condensers, resistors, a power source, etc., and is constructed such that the movable leaf contact piece 2 is separated from the contact 3a of the stationary leaf contact piece 3 upon depression of the key so as to start discharging operation, so that the voltage at the time when the movable contact piece 2 is contacted to the contact 4a of the stationary contact piece 4 is held by a peak hold circuit (not shown), resulting in obtaining a tone generation signal based on such a voltage signal. This circuit arrangement is so operated that the stronger the key depressing pressure is, i.e., the longer the key depressing speed is, the higher the peak-hold voltage is maintained. Thus, the initial control of the key for the instrument is conducted by detecting a period of from separation of the movable contact piece 2 from the stationary contact piece 3a to contacting of the contact piece 2 with the stationary contact piece 4a. However, the aforedescribed leaf switch mechanism requires high accuracy in bending work of the respective leaf contact pieces resulting in difficulty in manufacturing thereof. Other problems reside in production, check and maintenance of the switch such that even a casual finger touch on the leaf contact pieces exceeds the elastic limit of the contact pieces resulting in deformation of the pieces, and, accordingly treatment or manipulation of the switch requires great care. Furthermore, since the intrinsic or characteristic frequency of the leaf contact pieces themselves is high, it has such disadvantage that a chattering occurs at the switching operations of the switch.
There have heretofore been developed various touch response sensors for generating a signal responsive to the key depressing pressure required for the providion of the touch response effect, especially the after-control effect by utilizing a piezo-electric element, an electromagnetic induction, change in contacting resistance, etc., but any of these sensors had disadvantages such as expensive cost, complicated construction resulting in difficulty for miniaturization thereof, and accordingly satisfactory components could not be obtained for the conventional touch response sensors in every key of the musical instrument.